epa03942299 Indonesian officers gather near the ambulances as they receive the victims following an Indonesian army helicopter, MI-17 crash on the border of Malinau at a Hospital in Tarakan, East Borneo, Indonesia, 09 November 2013. An Indonesian official said that at least 13 people were killed and six people were injured when an Indonesian army MI-17 helicopter carrying construction workers to build a military outpost crashed and burst into flames in the jungles of Malinau, East Borneo. EPA/STR

A helicopter used by the Indonesian Search and Rescue (SAR) team, carrying people injured in a helicopter crash, prepares for landing in Tarakan on November 9, 2013. Thirteen people died when an Indonesian army helicopter carrying construction workers to build a military outpost crashed in the jungles of Borneo on November 9 and burst into flames, an official said. (AFP Photo)

Balikpapan/Jakarta/Tarakan. Indonesian rescuers were set Sunday to fly into the jungles of Borneo to evacuate the bodies of 13 people killed when an army helicopter crashed and burst into flames a day earlier.

Six people were also injured when the aircraft, carrying construction workers to build a military outpost, smashed into a cliff as it attempted to land at the remote site near the Malaysian border.

On Sunday four aircraft were set to fly to the area in Malinau district, North Kalimantan province, which can only be reached by air or river.

Two helicopters carrying chainsaws and mountaineering equipment would head first and a second helicopter and small plane would follow later to pick up the bodies, a military spokesman said.

"The rescuers' priority today is to retrieve the bodies and evacuate them from the crash site," spokesman Legowo Jatmiko told AFP.

"They will have to cut through wood with chainsaws and use ropes and mountaineering equipment to get to the bodies on the steep cliff."

He added that everyone was "ready but the problem now is the bad weather. It is cloudy and drizzling so we haven't been able to fly to the area yet."

President Susilo Bambang Yudhoyono expressed his "deep sorrow over the deaths of the soldiers and civilians."

"Hopefully the families of the soldiers and other victims will find fortitude in the face of this tragedy," he said in a tweet.

Jatmiko said rescuers also needed to retrieve the black box flight data recorders from the Russian-made Mi-17 aircraft, which was completely burnt out following the accident.

Once the bodies have been evacuated, an investigation into the cause of the crash will begin.

Military officials said they suspect the crash was caused both by bad weather and a problem with the back rotor blades, which appeared to spin out of control just before it hit the cliff. The helicopter appeared shaky as it attempted to land before the pilot lost control some 30 meters above the landing zone, Army spokesman Brig. Gen. Rukman Ahmad said.

Eight of those killed were civilian construction workers and five were crew members, who were military personnel. The six survivors were still in hospital receiving treatment for burns.

The helicopter had made several landings at the site in the preceding days as crews worked to construct an outpost along the Malaysia-Indonesia border, Rukman said.

"It was the eight time that the helicopter had flown there and there had never been any problems," he said.

Borneo is a vast, biodiverse island shared between Indonesia, Malaysia and Brunei, covered in lush jungle and home to rare animals such as orangutans.

There have been numerous fatal air crashes over the years in Indonesia and some have involved military aircraft.